After assembling a circuit board into an electronic device, an overall test is required to check the functions of the circuit board. The test mainly tests for defects such as an open circuit or short circuit, as well as for any substandard connections between the components under normal voltage, overvoltage, under-voltage conditions, or a serial interface. For example, a conventional testing system comprises an oscilloscope and a testing device connected to the oscilloscope. The circuit board comprises a serial interface and a plurality of pins corresponding to the serial interface. The oscilloscope is used to connect to the plurality of pins one by one by manually to be tested by the testing device.